1. Technical Field
The invention relates to a DC-DC converter and in particular, a series resonant DC-DC converter with improved load regulation.
2. Related Art
A DC-DC converter supplies a load with suitable power by stepping up or down a source voltage. A different load requires a different level of voltage. To change the level of voltage, the DC-DC converter incorporates a switching circuit that is turned on and off according to a predetermined duty cycle. The switching operation of the switching circuit often results in switching losses, which affect power efficiency of the DC-DC converter. A series resonant circuit may be used with the DC-DC converter (“series resonant DC-DC converter”) to substantially reduce the switching losses.
The series resonant DC-DC converter may include a transformer that transfers energy to a load. The transformer may include a parallel resonant circuit. The parallel resonant circuit may be formed from a parasitic capacitance and leakage inductance developing on a primary winding and/or a secondary winding of the transformer. The parallel resonant circuit may be naturally formed and transparent. The parallel resonant circuit may generate additional overshoot and/or ringing voltages. The additional overshoot and/or ringing voltages may result in excessive peak voltages. The excessive peak voltages may damage circuit elements connected to the transformer, such as a rectifier and a load. In addition, energy generated by the parallel resonant circuit may be wasted.
The series resonant DC-DC converter is suitable for audio applications because it may be lightweight and may have a high efficiency. In audio applications, a load is often an audio amplifier. The audio amplifier, as the load operates in a broad range, frequently operates at a reduced signal level. The peak voltages generated as a result of the parallel resonant circuit may severely damage a load such as an audio amplifier. Accordingly, there is a need for a series resonant DC-DC power converter capable of improved voltage regulation under all load conditions.